This invention relates to multicolor printing and is particularly useful in paper printers, such as strip chart recorders, which use registration elements which print through a ribbon onto paper. The printing may, for example, be carried out by an impact printhead, such as the dot matrix type, where a matrix of wires forms the impact elements or registration elements which provide for the impression of a multicolor record on the paper by the virtue of the registration accomplished by those elements through a multicolor inked ribbon. In recorders of this type the printhead is driven in traverse of the top of the chart drive roll or platen, and the multicolored inked ribbon is positioned in a plane parallel to the chart paper being printed on and between the line of traverse of the printhead and the plane of the chart paper. In recording or printing devices of this type, the multicolor ribbon is usually supplied in a disposable cartridge which has an endless ribbon with the majority of its length stored in a stuffing box, frequently elongated in shape, and having ribbon guiding arms projecting from its ends so that when the stuffing box is placed above and parallel to the line or plane of printhead travel the ribbon is guided through a plane parallel to the printhead travel and between the printhead and the chart paper.
In multicolor printing, when the printhead traverses the chart over a fixed path, it is necessary to selectively position the length of ribbon which spans the width of the chart, between the printhead path and the chart paper, in a manner so that the different color bands are selectively positioned under the printhead as needed for the printing of each color. Thus, the ribbon must be displaceable stepwise from a home position, in which the color in the band on an edge of the ribbon is printed, in a direction normal to the printhead path and in a plane parallel to the plane of the ribbon traversing the chart. This displacement must be carefully controlled in multiwire printheads in order to obtain proper registration. Thus, the wires or pins of the printhead must be positioned in each of the step positions so that the printhead will not print in two colors at the same time.
A prior art system which shows a multicolor printing recorder of the type described above is found in U.S. Pat. No. 4,654,672, issued on Mar. 31, 1987 to Kimura et al. In Kimura's strip chart recorder, as shown in FIG. 7, there is a ribbon cartridge which is mounted between two pivot points above the printhead with the ribbon following a path between the printhead and the paper. The cartridge has a sector gear mounted to it and that gear is driven so as to pivot the cartridge to thereby move the ribbon into the proper position for printing in each of the available colors. This particular system for moving the ribbon may be tolerated in a miniature recorder of the type shown in Kamura; for with a narrow chart, four or five inches, and with a printhead having a single wire as its impact element, the tolerance for the positioning of the ribbon is less stringent. With a multiple pin printhead, such as a nine pin head, and wider charts, such as 14 inches, the tolerance available for the positioning of the ribbon is considerably reduced. In other words, with a ribbon spanning 4 or 5 inches, it may be possible to move it with suitable accuracy by pivoting the ribbon cartridge, particularly when only one wire is used; whereas, with a ribbon of 14 inch length, it would not be easily moved with adequate accuracy using the same pivoting arrangement, particularly when multiple wires must be in registration with a single color band.
Still another method which has been used in printers for positioning a two color ribbon involves a solenoid actuated guide which has two positions corresponding to energization and deenergization of the solenoid and with a fixed ribbon supply rather than a pivoted cartridge. Such a system, of course, is not useful when more than two colors are involved, or when the space between the limit positions of the printhead as it traverses the paper and the fixed points of the ribbon support are close, for under those conditions the distortion of the normal path of the ribbon is too large for suitable operation to occur.
It is an object of this invention to provide a simple yet accurate positioning system for the ribbons of multicolor printers so that ribbon positioning, where more than one color is involved will be to closer tolerances than heretofore attainable and so that it is possible to have the limit positions of the printhead, as it traverses the paper, come closer to the guide elements for the ribbon, so that the frame holding the printer and the case enclosing it can be of a minimum width for a particular paper width.